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yes they can, this is where stretching comes in.

muscles are like strips of fibers. when we do resistant training, they build up. the strips of fibers get bulky and numbers of these fibers increase.

if you stretch well, u change the shape of these fibers and make them thiner and longer. thus even if the number of these fibers increases, the over all effect wouldn't change too much. the muscle is therefore more "dense".

of course, stretching wouldn't limit the effect of weight training. a big bunch of thinner strips of muscles could look bulky too. =) but more dense for sure.

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Riceball, all of the scientific articles that I have read contradict several of your statements. First of all, I have read that you are born with a finite number of muscle cells. You can't increase the number of muscle cells by strength training, you can only make the cells bigger. You can also make the cells bigger by drawing water/glycogen into them, which is why some folks think creatine makes your muscles look bigger.

I've also read that you can't stretch a muscle cell to obtain a long and lean look. You can lose fat, and have small muscles which will make you look long and lean, but at the cellular level, your muscles don't change by stretching. This can be disappointing for many women who want that "Yoga" body or think Pilates is going to make them look long and lean.

I'm open minded to contrary opinions if you have links to any scientific studies or articles that have shown you can stretch the muscle fibers.

My personal opinion based on the science I have read is that Ecala has it right. Muscles can do one of two things - get bigger or get smaller.

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conan, to be honest I haven't read much "scientific" journals reguarding muscles, but here is one that kinda hinted that muscle length could be increased by stretching. (tho the study was for other purposes)

http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1156528

truth is, I mostly read stuff on how to stretch certain area of muscles and help change the look of that part. and a lot of the stretching techniques do help me A LOT. What I said earlier is what I heard or read from other ppl..I'm not a real expert. but it does make sense and my result coincide with their theories.

here's a link where the "expert" answered some of the questions related to muscles.

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Here are some links, I'm kind of lazy so I just grabbed the first few that I found. There might be some better ones out there.

"There is a misconception that when you build muscle or add muscle mass that you are adding or increasing the number of muscle cells in your body. That is one hundred percent incorrect. It is physically and biologically impossible to add more muscle cells to your body. Of course science is doing crazy things these days so who knows what is on the horizon. But for now, you can not add muscle cells to your body.

What you can do is increase the size or volume of the muscle cells that you do have. Muscle cells require energy in order to function. The larger those cells are the more energy they will need. So where do they get this energy from? You have probably already guessed it, from your fat stores. As you can see by this example it is very important to increase your muscle's volume.

One of the reasons, although there are others, that the weight loss supplement creatine monohydrate is so affective in helping with weight loss as proven in many studies over the past ten years is that it shuttles water into your muscle cells giving them more volume. This increase in volume now requires more energy to burn in turn increasing your weight loss."

"Although you can not increase the number of muscle cells your body has (sorry people whatever your body has in terms of number of cells is all you get), you can increase their volume or size. When you do this the larger muscles need more energy to burn to maintain that size."

"The radioactive carbon-14 produced by above-ground nuclear testing in the 1950s and ’60s has helped researchers determine that the number of fat cells in a human’s body, whether lean or obese, is established during the teenage years. Changes in fat mass in adulthood can be attributed mainly to changes in fat cell volume, not an increase in the actual number of fat cells.

“If you are overweight and you lose weight, you still have the capacity to store lipids because you still have the same number of fat cells. That may be why it’s so hard to keep the weight off,” Buchholz said. "

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Conan is correct. We are born with a certain number of fat and muscle cells. These can be manipulated to grow or shrink. The only way to get rid of fat cells is to have lipo. In which case the remaining fat cells increase in size to make up the loss. Which is why so many that get lipo end up gaining weight again.

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The difference you guys are talking about (harder vs. bigger) is the difference between sarcoplasmic hypertrophy and myofibrillar hypertrophy. Sarcoplasmic is mostly just an increase in volume and fluid retention, whereas myofibrillar is an increase in the density of contractile fibers in the cell. People with fairly low muscle mass who are very strong exhibit myofibrillar hypertrophy, whereas swollen bodybuilders who can't lift that much are exhibiting sarcoplasmic hypertrophy. Different types of training and nutrition cause them.

http://en.wikipedia.org/wiki/Muscle_hypertrophy

You can also increase/decrease number of muscle cells. Myostatin deficiency causes the multiplication of muscle stem cells, but it also happens normally as part of training, or a number of diseases:

http://en.wikipedia.org/wiki/Hyperplasia

Adipocytes (fat cells) also do both. They tend to increase in size about 4x before they divide. Obese people therefore tend to have several times the number of fat cells that a thin person does. Additionally, obese people who then lose down to a normal weight don't really lose any of those fat cells. The degree to which some of them die off is still kind of an open question, but if they do it takes a while, and the hormonal influence of those extra fat cells (which each feels "emptier" than a fat cell in someone who's always been thin, since there's the same amount of fat divided amongst more cells) is thought to play a part in making it much easier to regain weight.